The present invention relates to a wide-angle telecentric projection lens system for use in enlarged projection at a magnification of about 15-20, that has a brightness of about F.sub.NO 1:7, and which covers a wide field of up to about 25 degrees in terms of the half viewing angle.
One technique for producing a large television picture is to project a small television picture onto a screen at an enlarged size. In this type of television system, generally referred to as a projection television system, separate B, G and R images are projected onto the screen via three respective lenses, with the B, G and R information being synthesized on the screen. Such television systems, however, have drawbacks in that, first, the need for three separate lenses for projecting B, G and R images results in a high cost, and, secondly, it is difficult to achieve alignment among the respective B, G and R images.
With a view to solving these problems, a television system has been proposed in which a color separating prism synthesizes B, G and R image information, which is then projected onto the screen using a single projection lens. The use of a color separating prism necessitates a telecentric lens, a known example of which is described in Japanese Patent Publication No. 63-1561. The telecentric lens system described in this patent is bright since its F number is on the order of 1:5. However, its half viewing angle of only up to about 12 degrees is too narrow to fully satisfy the requirement for overall size reduction for purposes of projection television. Thus, the telecentric lens system described in Japanese Patent Publication No. 63-1561 has a definite room for improvement.